Section 1 of 5The Idea of Pressure
Pressure describes how concentrated a force is over a surface.
Pressure
- The force acting per unit area on a surface, measured in pascals (Pa).
Force at right angles
- Pressure depends on the component of force acting at right angles to the surface.
Area
- For the same force, a smaller area produces a greater pressure on the surface.
Units
- One pascal equals one newton per square metre, written as N/m².
Section 2 of 5Everyday Examples
Pressure explains why sharp tools cut and wide shoes stop people sinking into snow.
Everyday Examples
Sharp knife
- A sharp blade has a very small area, so a small force creates a high pressure.
Snowshoes
- Wide snowshoes spread a person's weight over a large area, which reduces the pressure on the snow.
Tyres
- Inflated tyres spread the car's weight over the road, keeping the pressure within safe limits.
Drawing pin
- The point of a drawing pin has a tiny area, so the pressure under it is very high.
Section 3 of 5Using p = F ÷ A
Keep units consistent so that the answer comes out in pascals.
1
Write the equation p = F ÷ A, with pressure in pascals, force in newtons and area in metres squared.
2
Convert the area from cm² into m² by dividing by 10 000 if it is given in square centimetres.
3
Substitute the force and area into the equation and carry out the division.
4
Give the answer in pascals, or in kilopascals only if the question asks for kilopascals.
Section 4 of 5Worked Example
Question
- A box with a weight of 600 N rests on a flat floor.
- The base of the box has an area of 0.030 m².
- Calculate the pressure the box exerts on the floor.
- Write the equationp = F ÷ A.What the symbols mean: p = pressure (Pa = N m−2) · F = force acting at right angles to the surface (N) · A = area (m2)
- Substitute the valuesp = 600 N ÷ 0.030 m².
- p = 20 000 Pa.
Answer The pressure on the floor is 20 000 Pa, which is 20 kPa.
Section 5 of 5Exam Checklist & Tips
5.1.3 – Key Points for the Exam
- Pressure Force acting per unit area, measured in pascals.
- Pascal The SI unit of pressure, equal to one newton per square metre.
- Force A push or pull on an object, measured in newtons.
- Area The size of a surface, measured in square metres.
- Kilopascal A unit of pressure equal to 1000 pascals.
Common Mistakes
- Using an area in cm² directly in the equation without converting it to m² first.
- Calculating F ÷ p instead of F ÷ A when the question asks for pressure.
- Stating that a larger area always gives more pressure; for the same force a larger area gives less pressure.
- Describing pressure as a force; pressure is force per unit area and is measured in pascals.